Astronomers have discovered a barren cosmological orb 1.8 billion light-years wide.
Dubbed the “supervoid,” this immense stretch of relative emptiness (compared to the rest of the universe) helps solve one question scientists have been teasing apart for a decade. At the same time, it brings up a host of other questions that foreshadow an era of “exotic physics,” physics that will seem new and strange even to our most seasoned experts.
The supervoid has about 20% less cosmic material—galaxies, dust, etc.—than our part of the universe or any other area with typical density. It’s not exactly a void, since it’s not entirely empty. But when juxtaposed against other chunks of space, the supervoid appears a frigid wasteland.
“Frigid” may actually be the opportune word here. Scientists had been searching for a void in this region because they knew about the universe’s so-called “Cold Spot,” a part of the sky discovered 10 years ago that is unusually large and cold compared to what the CMB (cosmic microwave background) radiation—the thermal radiation leftover from the Big Bang—would have predicted for it. Over the last several years, they knew that if they could confirm that this part of the universe has a very low density, that would help explain why the Cold Spot exists, since photons speeding through an accelerating universe lose energy and cool as they cross a void.
Here’s Hannah Devlin, explains further at The Guardian:
This is because the photons convert kinetic energy to gravitational potential as they travel to the heart of the void and get further from denser surrounding patches of universe—think of it as climbing a hill. In a stationary universe, the situation would be symmetrical and so the photons would regain the lost energy on the way out of the void (down the hill). In an accelerated expansion of the universe, however, everything is effectively becoming less dense as space is stretched out, so voids become relatively shallower over time. This means by the time the light descends the virtual hill, the hill has become flatter and the light cannot pick up all the energy it lost on the way in. This means the light exits with a longer wavelength, corresponding to a cooler temperature.
To find the void, a team led by István Szapudi of the University of Hawaii at Manoa and András Kovács of the Eötvös Loránd University in Budapest calculated the number of galaxies in a patch of sky about 3 billion light years away from Earth. They used Hawaii’s Pan-STARRS1 telescope and NASA’s Wide Field Survey Explorer satellite to get an accurate measure.
Their results, published in the Monthly Notices of the Royal Astronomical Society, showed that there is in fact a huge, sparsely-populated region centered on the Cold Spot. Here’s Devlin again:
The structure may sound unremarkable—hardly a standalone object even—but scientists say it is unprecedented given how evenly distributed the universe normally is at this spatial scale. “This is the greatest supervoid ever discovered,” Kovács said. “In combination of size and emptiness, our supervoid is still a very rare event. We can only expect a few supervoids this big in the observable universe.”
Unfortunately, the void accounts for only 10% of the difference between the Cold Spot’s low temperature and other average temperatures in surrounding galaxies. So astronomers now have some new questions to ponder: What else might be contributing to the Cold Spot’s brittle temperatures? And how did the supervoid itself come into being? They will likely be addressed in the near future, but in the meantime, scientists will use this finding as added evidence for the presence of dark matter.